Maria Welch, a 52-year-old Baker City, Ore., resident who underwent surgery in July to remove most of her cancerous right lung, was in misery after doctors sent her home with some potent pain-killers.

The drugs deadened some of the pain, but left her nauseous, hallucinatory and suffering from sleepless nights.

"I felt like my body was asleep but my mind was awake. I just had to stop taking them because they didn't agree with me."

Then a friend gave Welch two marijuana brownies. Though she had never tried illegal drugs, she was desperate for relief.

"When I ate them I couldn't believe it. It was like a miracle. It took the pain away and it gave me an appetite," said Welch, a food industry researcher. "I slept like a log that night."

Scientists once scoffed at the claims of cancer patients like Welch that they enjoyed relief from pain by puffing on a joint of marijuana or gobbling a plate of pot-laced brownies.

But research during the past decade has buoyed the case for marijuana as medicine. Scientists have made progress untangling pot's chemical makeup and gained insight into how its ingredients act on the brain to produce the anecdotal benefits claimed by cancer, AIDS, glaucoma and multiple sclerosis patients.

Now research has confirmed what some of those patients have been claiming all along: Marijuana does indeed kill pain.

Scientists at the University of California at San Francisco found that a marijuana-like drug deadens pain in rats by interacting with the same pain-modulating area of the brain activated by morphine.

The findings prove that cannabinoids - which include marijuana's active ingredient, THC - are potent analgesics that deliver true pain relief, said Ian Meng, a postdoctoral fellow at UCSF's Department of Neurology.

In findings reported in the Sept. 24 issue of the journal Nature, the UCSF researchers describe how they injected rats with a synthetic cannabinoid to test how quickly the rodents reacted when a heat source was applied to their tails.

The drugged rats reacted more slowly to the heat than those not given the drug WIN55,212-2, and when a region of brain called the rostral ventromedial medulla that acts like a volume dial for pain was switched off, the drug's analgesic attributes ended, the team found.

A second set of tests demonstrated that it was the cannabinoid's pain-killing abilities - not the loss of motor coordination it also induces- that caused the rats to react slowly to their heated tails.

Meng said that given the findings, scientists should now push ahead and test cannabinoids on humans.

"People are smoking marijuana and giving anecdotal accounts. I think the time is here for real, controlled clinical trials," he said.

Proponents of the medical use of marijuana have claimed for decades that pot stifles chronic pain without the nausea, weight loss and addiction associated with morphine and other opiates.

The finding that cannabinoids target the same area of the brain as opiates, albeit through a different mechanism, raises the prospect that marijuana and opiates might be used together to exploit their combined analgesic qualities.

Using the drugs together in smaller amounts might also reduce the nausea caused by morphine and the euphoria sparked by cannabinoids that are undesirable in chronically ill patients, said Dr. Gavril Pasternak, who studies the biology of pain at the Memorial Sloan-Kettering Cancer Center in New York.

"I would say that it sounds reasonable that if used together the combination could work quite good," he said. "We know now that the brain circuitry can be activated by more than just morphine. So there's not a single key to make it work, there's two and maybe more keys."

Dr. Billy Martin, a professor of pharmacology at the Virginia Commonwealth University in Richmond who has studied cannabinoids for 25 years, said the UCSF team's findings are illuminating, but offer no magic bullet.

"This study is a little tiny piece of this whole big puzzle," Martin said. "...It opens up the possibility of developing new ways of treating and controlling pain and understanding pain, but it doesn't get us any closer to a cannabinoid pill tomorrow that's going to be useful."

Martin is one of several researchers who discovered that the human brain has a naturally occurring system that processes cannabinoids.

He said while scientists have made strides in understanding how marijuana's hundreds of compounds act on the brain to deliver the laundry list of benefits users claim to enjoy, the hardest work lies ahead.

Supporters of the medical use of marijuana who campaigned successfully for ballot measures legalizing its medical use in California and Arizona complain that the federal government has made advanced marijuana studies more difficult by erecting roadblocks to researchers.

The reason, they say, is that exposing marijuana's good side would undermine the government's war on drugs.

"The government has decided to wage a war against marijuana and they don't want any kinks in the armor. They don't want people knowing that marijuana, like morphine, has a medical use," said Bill Zimmerman, director of the Los Angeles-based group Americans for Medical Rights.

The nonprofit group is campaigning for medical marijuana measures that are on the ballot in five other states - including Oregon, where Welch must now travel to Canada to buy her marijuana brownies - and the District of Columbia this November.

The group's criticisms are unfair, said Dr. Frank Vocci, director of the medication development division of the National Institute on Drug Abuse, which co-funded the UCFS study. He said the reality is that the government has received very few proposals for research into marijuana and its components.

"Until there's more interest in this you can't really say there's a conspiracy because there's a dearth of applications," Vocci said.

The only human clinical trial under way involving medical marijuana is one that seeks to determine whether cannabinoids have any adverse effect on drugs being used to treat AIDS patients.

Meanwhile, the Institute of Medicine, a division of the National Academy of Sciences, is evaluating medical literature about the therapeutic value of marijuana and its chemical components.

It is expected to state whether medical evidence supports marijuana as medicine late this year or early in 1999.